The “Hydrogen Economy” is expected to grow continuously and hydrogen may eventually supplant fossil fuels as a primary energy source for many applications. Numerous hydrogen applications are being developed, including hydrogen-powered fuel cell or internal combustion vehicles, stationary power applications, backup power units, power grid management, power for remote locations, and portable power applications in consumer electronics, business machinery, and recreational equipment. A significant expansion of the Hydrogen Economy will require marked improvements in hydrogen purification techniques.
Because of their short useful life, polymer exchange membrane (PEM) fuel cells do not yet offer a commercially viable alternative to traditional power sources. The short lifespan of PEM fuel cells is attributable in part to membrane poisoning caused by the reaction of carbon monoxide found in a typical hydrogen gas stream with noble metals found in PEM's. In certain modes of fuel cell operation (e.g., running the fuel cell “dead ended”), the concentration of non-reactive trace impurities like nitrogen and methane can increase and the fuel cell requires periodic purging to remove the impurities. Thus, the more pure the hydrogen stream, the more reliable and efficient the fuel cell Since pipeline-grade hydrogen usually contains 1-10 parts per million (ppm) carbon monoxide, PEM fuel cells will be poisoned eventually by the carbon monoxide in a pipeline-grade hydrogen stream.
U.S. Pat. No. 4,477,267 (“'267 Patent”) describes hydrogen purification pressure swing adsorption (“PSA”) processes that use Ca-zeolite X granulate as an adsorbent. The PSA processes of the '267 Patent do not disclose the use of vacuum recovery of adsorbent, operate at low feed pressures, and achieve hydrogen recovery in the range of around 82%.
U.S. Patent Application Document No. US 20050257685 discloses the use of a continuous feed supply gas in a multiple bed PSA system, preferably a three bed hydrogen PSA system, that utilizes shorter beds having a lower adsorption pressure with an optimum ratio of product pressurization to adsorption pressure ranges from about 0.20 to about 0.35 for adsorption pressure from 20 psig to 900 psig from a 12-step cycle and 50 psig to 900 psig for other cycle steps.
U.S. Patent Application Document No. US 20020110504 discloses an apparatus for removing carbon monoxide from a hydrogen-rich gas stream. In one aspect, the hydrogen-rich stream is produced in a hydrogen fuel cell system which further includes membrane electrode assemblies where such hydrogen is reacted with oxygen to produce electricity.
U.S. Pat. No. 5,604,047 discloses methods for lowering the carbon monoxide content of a CO-containing, hydrogen-rich gas stream by contacting the gas stream with an adsorbent capable of preferentially adsorbing the carbon monoxide in the gas stream, the adsorbent being selected from the group consisting of platinum, palladium, ruthenium, rhenium, iridium, the carbides and nitrides of tungsten, molybdenum, vanadium, chromium, tantalum and mixtures thereof.
U.S. Pat. No. 5,955,214 discloses methods for lowering the carbon monoxide content of a CO-containing, hydrogen rich gas stream by contacting the gas stream with a scavenger capable of preferentially oxidizing the carbon monoxide in the gas stream and then regenerating the scavenger, the scavenger being selected from the group consisting of mixed oxides of manganese and copper; mixed oxides of manganese and copper in combination with mixed oxides of silver, nickel, iron and tin; mixed oxides of tin and copper; SnO2—CuO gels; and mixtures thereof.
There is a continuing need for improved and commercially practicable hydrogen and helium purification processes that can generate essentially carbon monoxide-free hydrogen and helium from, respectively, pipeline hydrogen and helium. Such hydrogen purification processes would make pipeline hydrogen a viable energy resource for PEM fuel cells, and in turn would increase the use of such fuel cells.